my $file = 'file.txt';
# open for input is default and now our die tells us which 
# file we were trying to open
open (DATA, $file) or die "Can't open $file $!\n";

# assuming you aren't using @DATA for something else later
# there is no need to slurp it all into memory now
while (<DATA>) {
  next unless $. > 21;
  chomp;
  my @temp=();
  foreach (split /,/){ 
    s/"//g;       # strip the quotes first if you want 
    s/\s+$//;     # to remove trailing whitespace 
    push @temp, $_;
  }

  $compHash{$temp[0]} = $temp[1];
  $aliasHash{$temp[2]} = $temp[3]; # you did mean $var4?
}
close (DATA);